1. Field of the Invention
This invention relates in general to crop irrigation. In particular, it relates to gates which are used to open and close outlet openings in irrigation pipe.
2. Description of the Related Art
In the irrigation of crops it is known to move the water into the fields through irrigation pipes, which typically have a circular cross section. At spaced points along these pipes openings are formed to allow the water to escape therefrom. To allow the fields to be selectively irrigated, these openings are provided with gates which may be opened and closed as desired. Examples of such gates are shown in U.S. Pat. Nos. 2,918,251, 3,455,533 and 3,989,224.
These patents show sliding gates which may be moved between extreme open and closed positions to control the discharge of water through the outlet openings of the irrigation pipes. Although this type of gate has performed in a generally satisfactory manner, it has not been wholly without problems.
In gates which have components formed of plastic or aluminum, the use of metal screws to maintain the component together have been a particular problem. Such screws corrode and tend to lock within the components, eliminating the ability to adjust or use the gates. In such situations the gate components typically must be broken to remove them from the irrigation pipe.
Additionally, where the gate components are formed of plastic, the metal screws tend to cut and otherwise damage the plastic threads. The result is a failure in the holding ability of the screw, which in turn causes leakage because the sealing element of the gate is not firmly held against the inside of the pipe wall. It is also not uncommon for the screw to loosen in service, creating similar leakage problems.
Gates in which the components are snapped together avoid the problems associated with metal screws, yet are subject to improper tolerances and size variations in service, causing leakage, and also are susceptible to separation when subjected to external forces. Also, this type of gate cannot be accurately adjusted as to the tightness with which it is held against the pipe.
Another problem with the gates that are currently available is their relatively high cost and their lack of versatility.